Apple was able to find worker bee using subpoenas from a court ordering Yahoo to turn over any data trails it had on worker bee.
According to the C-Net article:
In its suit, Apple alleges the defendant and possibly others posted information about Appleis new mouse and dual-processor PowerMacs before their introduction last month. Apple also said "worker bee" posted information to the AppleInsider site last month about a third product Apple has yet to introduce.
Although Apple named the worker in a court filing, News.com chose not to publish the name because Apple would not confirm whether he is the only employee with that name. An Apple representative also would not say whether the defendant still works at the company.
Apple said only that, "The protection of Apple trade secrets is incredibly important to our success. We intend to vigorously pursue legal actions that ensure the confidentiality of our intellectual property is not compromised."